Field of the Invention
This invention relates to a method to adhere thermoplastic elastomer blends to polyester substrates. The invention further relates to shaped articles obtainable by said method.
Polymer blends which have a combination of both thermoplastic and elastic properties (thermoplastic elastomers, TPE) are generally obtained by combining a thermoplastic polyolefin with an elastomeric composition in a way such that the elastomer is intimately and uniformly dispersed as a discrete particulate phase within a continuous phase of the thermoplastic. Early work with vulcanized compositions is found in U.S. Pat. No. 3,037,954 which discloses static vulcanization as well as the technique of dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured while continuously mixing and shearing the polymer blend. The resulting composition is a microgel dispersion of cured elastomer, such as butyl rubber, chlorinated butyl rubber, polybutadiene or polyisobutene in an uncured matrix of thermoplastic polymer such as polypropylene.
The inherent characteristic of the polyolefinic thermoplastic elastomer blends like all the polyolefinic thermoplastic is its non-reactive surface and consequently should be modified with a polar material in order to be cohesively bondable to polar substrates.
Polyolefinic thermoplastic elastomer blends as well as polyolefinic materials like polyethylene, polypropylene due to their low surface tension (28-30 dyns/cm) cannot adhere directly to more polar substrates like polyamid, polyester, metal and glass.
Various techniques are used to increase the surface tension of polyolefinic materials like chemical surface treatment, compound modification via polar ingredients, surface oxidation or to reduce surface tension of polar substrates by using a primer/adhesive system.
U.S. Pat. No. 2,911,321 describes a method for bonding a polyolefin layer on polyester using an "anchoring agent" of isocyanate/blocked isocyanate, which is applied to the substrate as a dilute solution in organic solvent. The polyolefin is extruded onto the treated polyester substrate and bonded by heat and pressure.
U.S. Pat. No. 4,345,004 describes a method of forming an olefinic coating on a (metal) substrate by applying a multi-layer film of epoxy resin, olefinic resin and modified olefinic resin, then heat bonding an olefinic resin layer thereto.
U.S. Pat. No. 4,732,632 describes a method of coating a substrate by applying a liquid, curable polymer composed of resin (e.g. epoxy; polyurethane precursor) and curative (e.g. isocyanurate) to the substrate, then applying a layer of polymer (e.g. polyolefin, EPDM, butyl, etc.) which can interact chemically or physically with the curable first layer.
Certain adhesion between a thermoplastic elastomer like Santoprene.RTM. rubber and polyester, polyamide is obtainable by using some solvent-based primer/adhesive systems like Morprime P80 from Morton International or Chemlock 487 from Lord Corporation. But the level of adhesion, obtained with these systems is not high enough for certain applications in dynamic conditions like power transmission. Also, the use of solvent-based primer/adhesive systems become subject to legislative restrictions based on environmental protection. Consequently, the development of the water-based primer/adhesive systems is highly challenged by most adhesive specialists.
It has now surprisingly been found that a method making use of both, modified thermoplastic elastomers and the pretreatment of the surface of the substrate yields excellent adhesion.
In detail the present invention relates a method to adhere thermoplastic elastomer blends comprising
(a) at least one thermoplastic polyolefin, PA1 (b) at least one non-cured, partially cured or fully cured elastomer or blends thereof, PA1 (c) a functionalized polyolefin and PA1 (d) optionally additives, PA1 treating the substrate with a blocked di-isocyanate in aqueous dispersion, or subsequently or simultaneously treating the substrate with a blocked di-isocyanate and an epoxy resin in aqueous dispersion/emulsion, PA1 applying the thermoplastic elastomer blend to the treated substrate and bonding the thermoplastic elastomer blend to the surface of the substrate using heat and pressure. PA1 (b) Olefinic Rubber PA1 (c) Functionalized Polyolefin
to a polyester substrate, said method comprising the steps of
Alternatively the functionalized polyolefin (c) may be applied to the polyester substrate prior to applying the blend of (a), (b) and optionally (d) to said substrate.